Welp, they got E2E encryption figured out, even between IOS and droid phones: RCS Encryption: A Leap Towards Secure and Interoperable Messaging - Newsroom Even more worried this becomes a missing feature with linux mobile in general [ping @linmob FYI]. It seems to be becoming the next generation in the line (SMS → MMS → RCS).
It would be good to have this as it would be a needed security upgrade (in addition to usability, although not the most secure nor private if you compare to other protocols). If you are using SMS based MFA, it may get hardened to RCS and stop working on linux phones (SMS MFA with security code is the most vulnerable, unlike one time pad type codes via SMS). That would effect a lot of essential services. It has been a whishlist ticket in Chatty for years, but no mention if it’s ever getting any love. I wonder if it could have some attention, now that phosh is in good order [adding a ping to @guido.gunther as the ticket owner]. To be fair, other open messaging apps are scrambling too (for example on F-droid side).
For those more interested on the scale of the task, Google dev docs: RCS Business Messaging 작동 방식 | RCS Business Messaging Developer Docs | Google for Developers A quote from Ubports blog from last year: “Most providers use a Google RCS server. We could in theory set up our own. Apple is moving into that sphere now too. It would be possible for us to use vendor supplied binaries but like VoLTE solutions, they would be device specific. Compared with VoLTE it is much less complex so perhaps there is potential there. It is a specialist area, so if you have knowledge or know someone who does, please contact us. Marius did a quick search and found that Google have provided packages in Node.js and Python.” [so, acceptably open version sounds doable]